Can't activate Facebook Ultimate

Even though PHP Curl is installed,
I get the following error:

Plugin could not be activated because it triggered a fatal error.

Fatal error: Uncaught exception 'Exception' with message 'Facebook needs the CURL PHP extension.' in /var/www/xxxx/wp-content/plugins/wpmu-dev-facebook/lib/external/base_facebook.php:19 Stack trace: #0 /var/www/xxxx/wp-content/plugins/wpmu-dev-facebook/lib/external/facebook.php(18): require_once() #1 /var/www/xxxx/wp-content/plugins/wpmu-dev-facebook/wpmu-dev-facebook.php(94): require_once('/var/www/xxxx...') #2 /var/www/xxxx/wp-admin/plugins.php(146): include('/var/www/......') #3 /var/www/xxxx/wp-admin/plugins.php(148): plugin_sandbox_scrape('wpmu-dev-facebo...') #4 /var/www/xxxxx/wp-admin/network/plugins.php(16): require('/var/www/xxxxx...') #5 {main} thrown in /var/www/xxxxx/wp-content/plugins/wpmu-dev-facebook/lib/external/base_facebook.php on line 19